Melbourne, Australia

The project is for my new garden pergola (just to give the plants under the pergola a pretty green glow at night time)

 

Its the battery recovering slightly when off load..

DONT damage your battery, charge it up PDQ...

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Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

what about the amount of batteries? If Im not supposed to let it drop below 10.8 then wont it go below that before the sun can get to it the next morning?

 

hi David,
The battery performance depends upon the AHr capacity of the battery, the current drawn from the battery and the general state of the battery.. its age and how well its been maintained and also the state of the 'charged capacity' when you start to drive your circuit.

Recharge your battery, upto 13.8V [14V absolute max.!]
Connect the circuit, cover the sensor so the leds are ON, observe the fall off of the battery voltage, STOP the discharge at 10.8V,,, note the running time.

To charge up the battery, using a solar panel you need to put the same current in for the same time * 1.5.

EDIT:
Obviously if you increase the recharge current the time comes down, but allow only 60% for the conversion efficiency.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

I think I need my batteries charging too, now

 

Well Jimmy,
Sit out in the English Sun and get a solar recharge.

__________________
Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

 

http://www.futurlec.com/Solar_Charge_Controller.shtml

This is a charge controller, also has a built in timer, and switches on after dark. It's exactly what you are looking for to charge your battery and turn on the lights. Will shut off when the battery gets below a safe level. The solar panel should produce 20v no load, and about 750 mA, for your 7.5 Ah battery. $26 and about 3 weeks, plus shipping. Not too bad, been working well for me.

Your relay probably consumes as much current as the LEDs, might be able to remove it, and drive the LEDs in it's place.

120 mA worth of LEDs, perhaps NiMh battery pack would be a better choice. Less worries about maintaining its charge level, and smaller solar panel.

 

are you saying that little gizmo will also swith on my LEDs at night? So I all have to do is plug my LED array in to it, plug in the right solar panel, turn it all on, and walk away?

 

Forgot the battery, but yes it's exactly what you are trying to build. I've got one, and works fine. Can't say if it will last all night though, but still going strong at 2:00 AM. I've got a 10 Ah battery, but going to get a boat battery eventually. Doing this for emergency lighting when the power goes out during hurricane season, maybe the coffee maker...

 

Anything that makes heat like a coffee maker uses a very high current.

Then you will need a huge and expensive solar panel, a huge and expensive battery and continuous sunshine every day without any hurricanes.

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Uncle $crooge

 

My little 4 cup (barely 2 real cups) claims 800 watts. Figure a 1200 watt inverter should work, but figure on finding a 12 volt coffee maker sometime. I've got a 12 watt solar panel hooked up right now. Want to see how it holds up to the weather here, before investing in a larger system.

 

What about getting a travel kettle and using instant?

A 500W kettle could boil 500ml (just under a pint) in 6 miniutes, in fact it's a bit less than that but I accounted for the heat losses.

It's not fast but it's good enough to make two cups.

The current rating would be 41.67A so use thick cable, 10mm² 7AWG and make it as short as possible.

This would take 41.67*6 = 250 Amp/miniutes = 250/60 = 4.167Ah.

It looks like your 10Ah battery will be fine and it shouldn't make much difference as long as the amount of water is the same - a higher powered element won't need to be on for as long.

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Instant? You can't be serious... I roast my own beans. Last time the power was out, I boiled some water over a propane cooker on the back porch.

Anyway, getting off the topic, and already hijack Hank's Dell thread this week.

There are a lot of other charge controllers available, and a few build your owns. The link I gave was one I bought and use. It small, inexpensive, and switches on the load at night. Just right for what I want to do. Most of what you will find are intended for powering more serious loads, and at a much higher price. That 5 watt model should be plenty, and could handle a lot more than 36 green LEDs if you want, or add some different lights later.

You can add batteries in parallel for more capacity. Not 100% sure about if its okay to mix capacities. Mine is 2 x 5 Ah SLA (had them sitting around). I've got a 12 Ah recently, and seems to hold a charge well, but haven't hooked in up yet. Have to see how much my 12 watt panel can handle charging in a day.

I don't remember your location, but you probably don't need a 12 watt panel, maybe 5-6 watts for here in Florida. I paid $114 shipped, for mine. It seemed like the best deal for what I was looking for.